Postage meters are well-known in the art and commonly include selectively operable alpha-numeric printing means for printing postal indicia on envelopes or the like. Typically two types of printing means are employed: one being a die plate that is adapted to print fixed information such as the town and state, while the other is a settable printing means which is adapted to print variable information such as date and postage amount. The variable printing means usually includes print wheels which project through suitable apertures formed in a curved die plate carried on the periphery of a drum. When the drum is rotated the printing die plate and the print wheels are suitably inked so as to be capable of imprinting on an envelope a composite postage marking.
In order to vary the postage amount and the date, a keyboard or similar setting means is normally provided to selectively vary the operative positions of the print wheels which are mounted to bodily rotate with the said drum. The setting linkage between the print wheels and the keyboard necessitates a rather intricate and mechanically complex arrangement to enable the print wheels to be first variably set to selected rotary positions from the keyboard and then be bodily swung through a rotary printing path determined by the movement of the printing drum.
In an improved postage meter of known design, as disclosed in commonly assigned U.S. Pat. No. 3,869,986 to Hubbard, the variable printing wheels and the associated setting linkages are dispensed with and replaced with an electronically controlled and actuated ink jet printing device. A drum carries an apertured printing die plate that is adapted to cooperate with a stationary ink jet printing device to produce a postage imprint. When a date aperture and a postage amount aperture in the die plate pass below the ink jet printing device, a plurality of ink droplets are sequentially ejected through the apertures and onto an envelope or label located at the meter print station. An electronic control is provided to actuate the ink jet printing device in timed relation to the movement of the die plate to form the required number and placement of the ink dots on the envelope to thereby establish the desired date and/or postage amount indicia. A drum position sensor is used to determine when the die plate apertures are properly aligned with the ink jet printing device and the postage receiving portion of an envelope or label. A print signal is then generated by the sensor and applied to the electronic control to initiate and sequence the ejection of the ink droplets.
By so incorporating a jet printing device in the postage meter the structural arrangement of the meter has been greatly simplified, and the mechanical complexity reduced to the point that a relatively simple efficient electronically controlled postage printing machine has been made possible.
The improved meter just described employs the die plate on the offset drum to provide the fixed information for subsequent application to the envelope or label while the ink jet printing device is used to print directly onto the envelope or paper. A fundamental problem in ink jet technology, however, has been in the ink/paper interaction. Since the ink wicks into the paper, much of the dye is drawn below the paper surface and hence does not contribute to the optical density. Also, the wicking is influenced by the paper's irregular surface resulting in non-uniform spreading and irregular edges. Another major problem with the patented concept has been the inability to make necessary corrections to the variable information prior to its application to the envelope or label.
In the past, various mechanisms have been devised for cleaning rolls or drums prior to the printing operation. Typical of such mechanisms are the disclosures in U.S. Pat. Nos., respectively, 4,135,448 to Moestue, 4,162,652 to Rebel et al, 4,236,450 to Bonomi, 4,311,095 to Jeschke, and 4,449,241 to Nakayama. Furthermore, U.S. Pat. No. 2,780,168 to Nichols discloses a specific liquid composition which can be applied to an offset printing mat to eliminate oil and grease smudges prior to the printing operation.